1. Field of the Invention
The present invention relates to a photovoltaic module, and is particularly suitable for a double-sided light receiving type photovoltaic module which receives light on both sides.
2. Description of the Prior Art
Photovoltaic power generation which converts light energy into electric energy by utilizing the photoelectric conversion effect is widely used as a means to obtain clean energy, which contributes to the preservation of the global environment. With the improvement in solar cells' photoelectric conversion efficiency, many photovoltaic power generation systems with photovoltaic modules have come to be installed even for residential use.
In order for a photovoltaic module provided with solar cells generating electric power from sunlight to output the generated electric power to the outside, conductors serving as a positive electrode and a negative electrode are disposed in the photovoltaic module, and ends of the conductors are taken out of the photovoltaic module as connection terminals to which cables for outputting electric current to the outside are connected, thereby extracting the electric current.
Connected parts between the connection terminals and the cables are accommodated in a housing called a terminal box for the purpose of protecting the connected parts and preventing leakage of the electric current. Usually, the terminal box is attached in the final process because the terminal box is obstructive during the production process of the module. The terminal box is adhesively fixed to the opposite side of a light-receiving surface of the photovoltaic module or is screwed to an outer frame of the photovoltaic module in order to reduce the weight load on the conductors, connection terminals and connected parts and to avoid looseness caused by vibration and metal fatigue.
FIG. 13 is a cross-sectional view of a relevant part of a conventional photovoltaic module. As illustrated in FIG. 13, the photovoltaic module 100 comprises a board-shaped photovoltaic submodule (photovoltaic panel) 50 including a plurality of solar cells 51, and an outer frame 60, made of aluminum or other materials, fitting over the edges of the photovoltaic submodule 50 through the intermediary of a sealing material 65. The photovoltaic submodule 50 includes the plurality of solar cells 51 interposed between a light-receiving side light-transmitting substrate 52 made of low iron tempered glass for example and a rear surface side weatherproof substrate 53. A sealing resin 54 such as ethylene vinyl acetate (EVA) fills the inner gap between the light-transmitting substrate 52 and the weatherproof substrate 53.
The outer frame 60 is made by extruding aluminum or the other materials and includes a main body 61 and a fitting part 62 located at the upper part of a main body 61. The fitting part 62 is in the form of a channel in a cross section and fits over the photovoltaic submodule 50. The main body 61 is hollow inside to save weight as well as being relatively thick-walled and robust. A terminal box 70 is adhesively fixed to the rear surface side substrate 53, with one side abutting the inner wall of the outer frame 60. If needed, the terminal box 70 is screwed to the outer frame 60.
In the photovoltaic module 100 with connection leads 55 taken out from an edge of the photovoltaic submodule 50 as shown in FIG. 13, the connection leads 55 connected to the terminal box 70 for extracting electric current is subject to damage because the connection leads 55 are interposed between the substrate 53 and the outer frame 60. Each connection lead 55 has an insulating coating on its surface since it may contact the metal outer frame 60. However, damage to the insulating coating of the connection leads 55 could cause an insulation failure. Thus, the conventional insulating coating needs to be thick enough to prevent the insulation failure caused by the coating damage, which increases the manufacturing cost of the connection lead 55.
A proposed natural lighting type photovoltaic module includes a light-receiving glass and a rear surface sealing glass, either of which is larger than the other, and a terminal box disposed on an expanded part of the larger one with consideration given to high quality in design (e.g. Japanese unexamined patent publication No. 2001-339087).
According to the above-disclosed Japanese unexamined patent publication No. 2001-339087, there is a space standing on a different level around the perimeter of the light-receiving glass or rear surface sealing glass. The space allows the terminal box to be attached thereon without affecting light-collection efficiency. However, the conventional photovoltaic module having the terminal box disposed on the expanded part of the glass cannot be adapted to a type of photovoltaic module in which the photovoltaic submodule is easily fitted into the outer frame, because of the obstructive terminal box.